I acquired an 'abandoned' base at a planet. The planet was unoccupied. I also got a Capital ship that was also abandoned there. I made the Capital ship a 'fleet of one' with the fleet posture to 'guard' the 'station' on manual control (because it kept running away when I put it on automatic).

Another Empire's colony ship sails in (one I have a mutual defense pact with), and with my ship sitting right on top of the planet, the other empire colonizes my planet!!!

What can I do to keep these other empires from colonizing planets at which I have a base/star-port with an attending 'fleet' or combat ships? Do I have to manually attack these ships until I actually have a colony of my own there or are there other tricks I can use? This has happened several times now and I'm getting more than a wee bit irritated.

As far as I can tell, everything is working as designed in what you described above, if that unoccupied planet was not in your sphere of influence. Those colonizers who colonized that planet were not attacking you. The planet is not "yours" until you colonize it. To answer your question: you have to colonize it and make it "yours", or colonize a planet close enough so that the place you want is within your ZoC. Also, I am guessing that you are not at war with whomever it was who colonized that planet, or your ships would have attacked automatically; you could change that, and hence chase away that friendly colonizer, but you can't do that when at peace. Get it?

I take pot shots at construction ships and colony ships to keep them away from areas that I want to reserve for me. I might take a reputation hit, but most of the time it will not start a war.

FoM

That's a fine theory, but so far I have had ZERO luck in getting my (*YUW#$(%*YE(T combat ships to attack much of anything. I click on the little bullseye, position it on the target ship and then the combat ships/fleet either do nothing at all or wander off somewhere. I've spent literally hours this evening trying to get them to attack colony ships, even military fleets I am at war with. To top it off, the game died on me and I lost what I had done.

Automation is OFF. You need manual control to give the attack order and make it stick. Otherwise your ship just flys off to another assignment. I just take a few shots until the colony ship begins to retreat, then I stop the attack. No need to completely destroy the colony ship. The other empire might complain a little, but don't worry about it.

Thanks Fisher. Only one problem. I didn't get the ships to quit firing quick enough and the colony ship was destroyed. I'm at a -74 with that empire now. Oh well...bet they won't send another ship in before I can get my own colony in place.

when you want to take pot shots, slow the game down to .25. when you see the shot leave the ship cause the ship to move away by hilighting the ship and clicking in empty space near the target. A single shot will cuase the target to jump away.